Trunking circuit to centralized operator&#39;s position



Nov.. 6, 1928. 1,690,234

v F. R. LAMBERTY TRUNKING CIRCUIT '1'0 CENTRALIZED OPERATQR'S POSITION Filed vD90 1927 5- ShQGtS-ShQBt F% III-III POL ARAZED 7 MAW/N4 IIHI- -M I IH /NVEN ran.- FREDER/UKRLAMBERTY ATTORNEY NOV; 6, 1928. 1,690,234

F.'R. LAMBERTY 'TRUNKIN'G CIRQUIT TO CENTRALIZED orr'znmonsfosrnon.

Filed Dec. 1927 5 Sheets-Sheet 4 lg'VVL-N TOR. FEEDER/0K RA AMBERT) DY ATTORNEY F. R. LAMBERTY TRUNKING CIRCUIT To CENTRAL'IZED OPERATORS POSITION Nov. 6, 1928.

Filed Dec. 6, 1927 5 Sheets-Sheet 5m 4E ag E l vl/f/vro/i' FREOERIC/F/QLAMBERT; BY

Arm/m5) change systems and more particularly to. dial coin collecting or r'e systems in which 'the, connections to toll points are'establi shed through an operators made 'for-reli hting the trunk lamp at the sition and toll is assessed. against calling A board if t e operator disconnects before 55 the-icalling subscriber hangs up.. a

- 'In the embodiment of the invention chosen with their lines.' Theobject. ofthe invention Pueiited- Now. 6, 192's;

UNITED STA E PA ENT om n.

rannnmcx a antes-arr, or naoox'm'm, imw roaxmssmnon 'ro BEL-L 'ramrnour. mona'roms. mcoaroaa'ran, or NEW roam-rr, x'coaroaarrou' or mew YORK. 'IBUH'KDTG CIRCUIT '10 CINTBAIIIZED OPEBAIOBS PQSITIOIL.

Application filed December a, 1m. er at. 238,007.

This invention. relates to telephone expilot lamp 1 at-the ofplerators position when subscribers by means ofcoin boxes assoc ate mitted to the coin box.

is the provision of improved trunk circuits for for thepurpose of illustration, the callingv extending connectlons from calling lines to subscr ber whose line is equipped with a an ,operators position which Wlll enable the co n box, uponiinitiating a call becomes con 60 collectthem if the call is successful or to reing end-o i switching A board which is arranged teen P tViS Y and-to enable theoperator to control thecoin is responsive to the oflice battery current, and 7 box to collect or refunddeposited coins by thetwo remaining relays being responsive operator to control coin collection or' refund nected over'the usual swltching equipment from the usual coin keys ofher cord. circuit; with a trunk circuit terminating in a\first with greater facility and over the connection selector switch. This selector trunk circuit established to the operatofis position by lthe calling'subscriber. i

,is provided withfthe usual equipment for conthe .com box eqhipment. The subtrolling to obtain a toll connection,-.then dials 'In telephone exchange systems employing scriber,

machine switching apparatus for extending zero setting the first selector on an idle trunk connections between subscriberslines, it 19 Ma customary to provide sci-called machine ing switching A operators-positions for the purf plurali pose of aiding subscribers in extending ce r ,7 trunk oup extendin' to the machine switchboard whic is made common to a ty, of ofiices in the exchange area. The circu ts of-this group and in which tain' types of connections, particularly conthe present invention centers are of the charnections to toll points. In such systems a acter of interoflice trunks and are, therefore, subscriber desiring a toll. connection. dials of the two-conductor type.

zero. and becomes connected over a first selec- Each trunk, at either end-thereof, is pro '15 tor switch to a trunk circuit terminating at an vided with a high resistance bridge and with j .operators position on the'A board. -The line relaysfor reducing the resistance of each operator answers the call and after receiving bridge for controlling supervision. Wheninstructions from the calling subscriber exthe trunk tends the connection to the desiredtoll point, a selector and the A operator has responded-bjplugging into the jack. in which the d of the trunk terminates, both On such toll connections it is desirable, if

the calling subscribers line is eqgipped with a incom ng en is seized at its: outgoing end by coin box, to require the subscri er to deposit bridges become efiecti e. Since the calling} the number of coins which the operator tells subscribers receiver is oil the switchhook, the him is necessary, before the deslred connecline relay atfl the outgoing end of the trunk tion is completed. After the coins have been reduces the resistanceof the bridge thereat, deposited provision must then be made to thereby causing the line relay atthe incomfund any deposited coins if the call is unsuc sitance of "cessfulr The present invention relates to a of the resistance of the second bridge permits 6 f the trunkto also redueethe rethe bridge thereat. The reduction two-wire trunk for connecting a machine the operation of the answering cord superswitching ofiice: to a centralized machine visory, relay to extinguish the answeringsu able the control of the usual switchhook su- 'pervision between the subscribers? lines and cry lamp. p p y The bridge at the outgoing end'of the trunk comprises threedouble'wound relays, onegof thesanswering c'ord' circuit at the A board, which serves as a trunk holding relay, an

means of the coin ke sot 'hercord circuit, only to .voltcoi box currentapplied by.

Provision is also ma e for operating a coinfthe coin keys at the A? Oneof these mo ,of the cord circuit may g ltgqing end of the trunk circuit and to the be transmitted to the has l itthe outgoing end 0 -25 application of latter relays is'negatively polarized for response to negative 110 volt current and the other is positively polarized and res onsive to positive 110 volt current. When t e A operator desires to either refund or collect a coin' in the calling line coin box, she operates the' proper coin key at her position thereb applying either 110 volt positive or 110 v0 t negative current to both the ti and ring conductors of her cord circuit and t ence to ground through both .windings of a relay in the bridge at the incoming end of the trunk. This relay, which is not responsive to current from the cities battery, does respond to 110 volt current applied by either of the operators coin keys, and in turn causes the tip conductor of the come) grounded and the ringconductor to. be connected around the trunk condenser," so that the 110 volt current applied to the ring pass directly to the -p arlzed relays in brid e thereof.

' %the trunk circuit the flo volt current flows serially through all of the win of the, bridged relays. If negative 110 v0 trcurrent has been applied to refund the coin, the negatively polarized relay of the bridge operates and in turn causes the 110 volt refunding current 0111 a source local to the trunk circuit to coin box of the calling line. Similarly if positive 110 volt current been applied to collect thecoin, the positively polarized relay of the bridge operates and in turn causes the a plication of 110 volt collecting current to e transmitted. In

, either case when current is thus applied to a pilot lamp is lighted switchhook, the bridge the trunk circuit is, under the nt-ro of the associated line relay increased in resistance the coin x, means is provided at the outgoing end of the trunk circuit to short-circuit one winding of each of the bridged relays to reduce the resistance of the bridge, whereby at the operators position to indicate ,that current has been applied to the coin box.

At the termination of the call, when the ca g subscriber returns his receiver to the at th e'ou t oi end of and thereby the brldge at the incoming end of the trunk circuit is also increased in re-- sistance. The cord supervisory relay-can not remain o erated in sistance' ridge at the incoming end of the trunk circuit and thus releases causing the illumination of the answering cord lamp as a disconnect signal.

Referring to the drawings, ig. 1 shows a calling line terminating in a line switch, and a coin box controlling trunk circuit;

Fig.2 shows a first selector circuit in which the trunk circuit of Fig. 1 terminates;

Fig. 3 shows the outgoing end of a trunk 5 .circuit extending to a centralized A interoflice trunk to bethepontact of 'erg1zing,-in turn closes a circuit for relay 103,

series with the high re- -'lector extending from battery,

operators position;

Fig. 4 shows the incoming end of the trunk circuit shown in Fig.3; and

Fig.5 shows one cord circuit at an A operators position.

It is believed that the invention will be best understood through a consideration of the establishment of a connection from the subscribers substation 100 of Fig. 1 to the A operators position of Fig. 5. For this purose the several figures of the drawing should e arranged end to end in consecutive order with Fig. 1 at the left and Fig. 5

Establishing connection.

The calling subscriber at substation 100 to initiate a call removes his receiver from the switehhook there y causing the line switch 101 in which the subscriber 5 line terminates to connect with an idle trunk shown in Fig. 1. The line switch 101 has been diagrammatically illustrated herein but may be of a well-known type such as is disclosed for example in Patent 1,304,369, issued to A. J. Ray on March 20, 1919. It will be assumed'that the trunk line shown in Fig. l is idle and becomes connected by the line switch 101 to the substation 100. A circuit is thereupon established for the line relay 102 extending from ground through the outer left back contact of relay 103, winding of relay 102, coil 104, inner left back contact of relay 105, upper normal contacts of relay 106, tip rush of switch 101, over the substation loop returning over the ring brush of switch 101, lower normal contacts of relay 106, right back contact of relay 105, inner right normal contacts of relay 103, resistance 136, right normal contacts, of relay 107, to battery throu h the inner right back contact of relay 108. elay 102 cuit for relay 109. extending from batter the right back contact of relay 110, win in of relay 109 to ground at the front contact 0 relay 102, and a circuit for relay 111 extending from battery at the right back contact of relay 110 through the winding of relay 111, the right back contact of relay 112, the inner left back contact of relay 103, to ground at relay 102. Relay 109, upon enextending from battery. at the left back contact of relay 107, windin of relay 103 to ground at the contact of re ay 109. With relay 109 energized the circuit of relay 111 is connected directly to ground at the innerleft alternate contact of relay 103.

Relay 103, upon energizing, establishes a circuit for the line relay 200 of the first seleft winding of relay 200, uppermost lower back contact of relay 201, conductor 202, lower normal contacts of relay 1'13, conductor 114, right at the right such as is.

upon energizing, closes a circontacts of rela front contact of relay103, retard coil 115, conductor 116, Winding of polarized relay 117, upper normal contacts of relay 113, conductor 203, inner upper back contact of relay 201, through the right winding of relay 200, the normally closed contacts of the 11th rotary step springs 208 to ground through the dialing tone coil 209. Relay 200 energizes, closing a circuit for slow release relay 204 extendingfrom battery through the winding of relay 204, the front contact of relay 200 to izround at the uppermost back contact of reay 201. Relay 204 at its right front contact prepares a stepping circuit for the vertical magnet 205 in series with the slow-to-release relay 206 and at its left front contact places a busy holding ground on the sleeve conduc-- tor 207. Relay 103 upon attracting its inner right armature substitutes relay 122 for resistance 136 in the ring side of the calling line circuit but relay 122 being marginal does not operate .at this time.

Dialing tone now passes from the coil 209 as traced over the tip trunk conductor 203,

through the Winding of relay 117, conductor 116, resistance 118, inner upper front contact of relay 111, condenser 119, upper normal line returning t rough the lower normal contacts of relay 106, condenser 120, inner lower front contact of relay 111, resistance 121 conductor 114, thence to battery through the left winding of relay 200 as previously traced.

The subscriber hearing the tone proceeds to deposit a coin in the coin box chute preparatory to dialing; The coin box may be of the type shown and described in Patent 1,043,219, of November 5, 1912, issued to O. F. Forsberg. As shown and described in de tail in said patent the deposited coin causes the closure of contact 123 to ground the tip side of. the line and since the receiver is now removed from its hook this ground is also connected to the ring side of the line. The application of, this ground closes a shunt about relay 102 and causes its deenergization, whereupon the marginal relay 122 opcrates over a circuit including the ringside of the line, the calling substation receiver hook and the ground closed at contact 123 ofthe coin box.

106, thence over the calling closes a circuit for over the same front contact, the outer left back contact of relay 105 to ground through the winding of relay 107. Relay 124 upon operating also closes an obvious circuit for operating relay 107 independent of the contacts of relay 105. At its outer left front contact relay 108 closes a shunt around re sistance 118, a shunt about resistance 121 be- .ing closed at the right back contact of relay l close'd at the left contacts of relay to prevent the relay 200 of the first selector from releasing. At its right :contact relay 125 closes an obvious circuit for' slow releasing relay 112 which, in turn, extends operating ground from the right front contact of relay 125 through the frontcontact of relay 112, winding of relay 111 to battery at the right normal contact of relay 110. The circuit1 is1 now ready for the calling subscriber to ia v In response to dial impulses relay 125 fol-- lows the impulses, but relay 112 being slow to release does not deenergize duringimpuls- 'lng. Upon each deenergization of relay 125 in response to each dialing impulse, the bridge previously traced across trunk conductors 114 and 116 is opened at its left contacts, thereby permitting relay 200 of the first selector to release. Upon each release of relay 200 a' circuit is closed from ground at the upper back contact of relay 201, back contact of relav 200, right front contact of relay 204, which relay being slow to release does not deenergize between impulses, winding of relay 206 to battery through the windingv of vertical magnet 205.. Magnet 205 operates to step the switch brushes vertically one step each time that relay 200 deenergizes in response to an impulse from the calling dial and relay 206 being slow to release remains energized until the series of impulses is terminated.

Upon the initial vertical step of the switch shaft the off-normal contacts 210' close and with relay 204 energized, a circuit is closed for relay 211 extending from battery, winding of relay.211', off-normal contacts 210, front contact of relay 206, to ground at the left contact of relay 204. Relay 211 prepares the circuit of the rotary magnet and looks over the off-normal contacts 210, back contact of rotary magnet 213, left contacts of relay 211 to ground at the upper contact of relay 201.

Since a connection to the A operators position is under consideration, it will be assumed that the calling subscriber dialed the digit zero and that therefore the first selector was operated to position its brushes opposite the tenth level of its bank.

Following the termination of the impulse series, relays 200 and 204 remain energized and after an interval relay 206 deenergizes. A circuit is now closed for the rotary magnet 213 extending from battery, winding of magnet 213, right front contact of relay 211, normal contacts of relay 206 to ground at the left contact of relay 204. Magnet 213, upon operating, opens the locking circuit of relay 211, whereupon relay 211 deenergizes in turn opening the operating circuit of magnet 213. The switch brushes are thus advanced in a rotary direction into engagement with the first set of trunk terminals in the tenth level. If the trunk in which this set of terminals terminates is busy, there will be ground potential on the sleeve terminal engaged by brush 212 and relay 211 will be again operated from ground on the brush 212, over the lower back contact of relay 201, the back contact of magnet 213, off-normal terminals 210 to battery through the winding of relay 211. Relay 211 will again close the circuit of magnet 213 which will operate again, opening the circuit of relay 211, thus advancing the switch brushes to the next set of trunk terminals. In this manner the switch brushes are advanced until an idle trunk is encountered, which trunk will be assumed to be the one disclosed in Figs. 3 and 4.

Relay 201 which has been shunted as long as the brush 212 encountered grounded sleeve terminals of busy trunks now energizes in a circuit from battery, through the winding of relay 211. off-normal terminals 210, the back contact of rotary magnet 213, winding of relay 201, normally closed contacts 214 of the eleventh rotary step springs 208 to ground at the left contact of relay 204. Relay 201 be-- ing of high resistance relay 211 does not opcrate in series with relay 201. Relay 201 at its inner front contacts connects the trunk conductors 203 and 202 over conductors 216 and 215, brushes 217 and 218 to trunk conduct-ors 219 and 220, respectively, disconnects the windings of relay 200 from conductors 202 and 203 at its inner back contacts thereby releasing relays 200 and 204, disconnects operating ground at its uppermost back contact and at its lowermost front contact, cor.- nects the sleeve conductor 207 directly through to sleeve brush 212, thence to the sleeve conductor 305 of the selected trunk circuit. Ground is applied to conductor 305 as will be presently described before slow-torelease relay 204 has time to completely release so that ground is supplied to conductor 207 without interruption and relay 201 is maintained energized over the circuit previously traced through its winding, thence through contacts 214, the lower front contact of relay 201 to ground on conductor 305.

Upon the seizure of the trunk 219, 220 a circuit is established for the relay 300 which extends from battery, winding of relay 3%, lower left winding of repeating coil 301, lower back contacts of relays 302 and 303, conductor 220, brush 218, conductor 215, innermost lower front contact of relay 201, conductor 202, lower normal contact of relay 113, conductor 114, left front contact of relay 125, retard coil 115, conductor 116, winding of rela 117, upper normal contact of relay 113, con uctor 203, upper front contact of relay 201, conductor 216, brush 217, con ductor 219, upper back contacts of relays 303 and 302, upper left winding of repeating coil 301, resistance 320 to ground. Relay 300 energizes, closing an obvious circuit for relay 304. Relay 304 places ground on the sleeve conductor 305 to hold the preceding selector from releasing. Relay 304 also closes a circuit to operate relay 306 which may be traced from battery,througl1 the winding of relay 306, the lower back contact of relay 309 to ground at the contact of relay 304.

Relay 306, upon energizing, closes a circuit for operating relay 307 which. extends from battery through the winding of relay 307, the upper normal contacts of relay 309 to ground at the armature of relay 306. Relay 307, upon operating, establishes a circuit over the two conductors 310 and 311 of the trunk extending to the A operators position for operating the relay 400 in a circuit which may be traced from battery, upper winding of relay 309, upper front contact of relay 307, upper right winding of repeating coil 301, conductor 310, upper back contact of relay 401, winding of high resistance relay 400, lower back contact of relay 401, conductor 311, lower right winding of repeating coil 301, lower front contact of relay 307 to ground through the lower winding of relay 309. Relay 400 energizes in this circuit, but relay 309 being marginal does not operate due to the high re sistance of relay 400. Relay 400 closes an obvious circuit for the trunk lamp 402.

In order that the calling subscriber may be apprised of the fact that the operator is being signaled, relay 307, upon operating, connects the source of ringing current 308, over its lower front contact, the lower back contacts of relays 302 and 303, thence as traced to conductor 114, right back contact of relay 103, innermost lower front contact of rela 111, condenser 120, lower normal contacts 0 relay 106, thence over the calling line, returning over the upper normal contacts of relay 106, condenser 119, upper front contact of relay 111, left front contact of relay 108, conductor 116, thence as traced to ground through the resistance 320. a

In response to the lighting of trunk lamp 402, the A operator inserts the answering plu 500 of a cord circuit at her position into the-pick 403 of the trunkto which the lamp 402 is individuah'closing a circuitextending from battery, winding of sleeve relay 501,- sleeves of plug 500 and jack 403 to ground through the winding of relay 401. Relay '401 energizes, disconnecting the winding of relay 400 from the conductors 310 and 311 of the trunk circuit and through its upper and lower front contacts, respectively, connects grou'nd to -conductor 310 and battery to 'conductor 311, through the back contacts of relay 405 andthe windings of relay 404. It is to be notedthat battery is. now connected .to the ring conductor311 of the trunk, through the lower winding of relay 404 and ground 1s' connected to this trunk conductor through the lower winding of relay 309, and that round is connected through the upper win in of relay 404 to the tip conductor 310 and attery to the same conductor through the upper winding of relay 309. Relays 309 and 404 both operate in this circuit.

Relay 309, upon operating, locks throu h its upper alternate contact to ground at the contacts of relay 306 and opens the circuit of relay 307 which now releases, disconnecting. the ringing tone asasignal that the operator has answered the call, and bridging the lower windings of relays 312, 313 and 314 in series across the trunk .conductors 310 and 311.

This bridge extends from conductor 310,

through the upper right winding of coil 301,

the upper b'ack contact of relay 307, the lower front contact of relay 300, the rightback contact of relay 316, the right back contact of relay 317, conductor 315, the lower windings of relays 314,313 and 312, the lower bac k con tact of relay 307, the lower right winding of coil 301 to conductor 311. The upper windings of relays 312, 313 and 314 are not effective at this time being shunted by the lower front contact of relay 300. Relay 404 is held energ'ized over this bridge.

-'It is. to be noted at this point that PI'IOP'tO' the response of the operator/there was a wet bridge of'the trunk conductors 310 and 311, through the windings of relay 309 at the outgoing end of the trunk and a dry. brldge through the winding of relay 400 at the incom- .ing end thereof Relax and that upon theres onse the wet bridge thrpug the 404 became substituted for the incoming end of the y I through the windings of relays 312 313 and 314 was substituted for the wet bridge through the windingsof relay 309 at the outgoing end of thetrunk. s 313. and 314 do not operate on curstren th Qver'the bridge (i but relay 312 op} of the operator, windings of relay the dry bridge at trunk and a drybridge rent 0 signalling circuit jreviously trace erates c osing a holding circuit for rela 306'- to replace the operating circuit throng the back contactof relay 309 which was opened upon the energization of relay 309, and establishing anew holding circuit for sleeve relay 304. Relay 306 being slow to release does not have time to completely deenergize following the opening of its circuit by relay 309 before relay 312 closes the new holding circuit through its winding.

At the incoming end of .the trunk circuit when the operator inserted the plug 500 into the jack 403, a circuit was established extending from battery, through the winding of answering supervisory. relay 503, the lower. back contact of relay 504, the lower left wind 'ing of repeating coil 505, the lower back contact of relay 506, the lower normal contact of key 507, rings of lug 500 and jack 403, the lower winding of retard coil 408 and the lower winding of relay 409 to ground. Relay 503 does not operate in this circuit due Y to the high, resistance of relay 409, but upon the operation of relay 404 a shunt upon both .windmgsof relay 409 isclosed, thereby permitting relay 503 tooperate. Relay 503, upon operating, shunts the supervisory lamp 502 which became lighted upon the operation of the sleeve. relay 501' and this lampusthere upon extinguished. I r

- Relay 309 at its lower front contact closes a circuit for the reversing relay 303 extend- 'ing, from battery through the winding of relay303, lower front contact of relay .309, tov ground at the front contact of relay 304. Re-

lay 303 upon operating reverses the connec tion of ground and battery through resist ance 320 and relay 300 to the trunk conduc tors 219 and 220 whereby the current fiowin through the winding of polarized relay, 117 is now in the proper direction to operate re lay 117. Relay 117 upon operating closes a circuit for relay 126 extendingfrom battery through the winding of relay 126, right nor-- mal contacts of, relay 126, contact of relay 117, to ground at the outer left front contact of relay 107. Relay 126 upon operating opens its own operating circuit and locks irectly no to ground at the outer left contact of relay 107. A circuit in parallel with the energizing circuit of relay126 is also closed through 1 the back contact of relay 127 and the winding of relay 113 to battery. Relay 113 upon op: 115 erating reverses the connection of the trunk conductors 202. and203 to the conductors 114 and 116 thereby causing relay 117 to deener- .gize, and at its lowermost front contact closes a; circuit for relay 127 extending from bat- 12o "tery, winding of relay 127,.lower frontcontact of relay 113, to ground" at the outer left front contact of relay 107. Relay 113 also closes a locking circuit for itself .over its lower front contact. Relay 126 upon oper- 1 the plug through the front contacts of relayv 506 in parallel to conductor 509, thence tors 114 and 116 become connected directly over the brushes of the line switch 101 to the calling line conductors.

I Refunding the deposited coin.

It will first be assumed that the operator does not desire to charge the calling subscriber for the desired connection and wishes to refund the coin which-has been deposited in the coin box. The operator then proceeds to refund the coin by depressing the refund key 508. When this key is operated a circuit for the relay 506 is established extending from battery through the winding of this relay to ground at the left contact-of key 508. Relay 506 upon energizing disconnects signaling battery from the tip and ring contacts of plug 500 and connects the tip and ring of through the right alternate contact of key 508 to the 110 volt source oflnegative refunding potential 511 through the winding of relay 510. Current from the source 511 flows over the tip and ring contacts of jack 403 in parallel through the windings of relay 409 to ground regardless of whether the calling subscribers receiver is off the hook and relay 404 is still energized, or whether the receiver ison the hook and relay 404 is deenergized.

Due to the high resistance of relay 40.9 the relay 510 does not operate at this time to close the circuit of the coin pilot lamp 512. Relay 409 operates, however, closing an obvious circuit for relay 405 which disconnects the windings of relay 404 from trunk conductors 310 and 311, connects direct ground to the trunk conductor 310, and connects the trunk conductor 311 through the lower front contacts of rela s 401 and 405, through resistance 410, to cond hctor 407 ,'thence to the 110 volt sourc "of negative potential 511.

Current from the source 511 now flows over the ring conductor 311 of the trunk to round as traced through the lower windingsof relays 312, 313 and 314 causing the operation of relay 312 and of the polarized relay 313 which is poled to respond to 110 volt negative current. Polarized relay 314 being poled 0p-' positely does not respond. Relay 313 upon energizing operates relay 316 in an obvious circuit which latter relay upon energizing removes, at its right contact, the shunt from the upper windings of relays 312, 313 and 314, c oses an obvious circuit for relay 302 atits inner left contact, and at its outer left contact connects the 110 volt source 321 of coin re-- funding currentthrough the winding of relay 322, the front contacts of relay 302 in parallel, thence to the tnmk conductors 219 and 220.

Upontlie energization 'of relay 302 theline relay 300 is removed from connection with the incoming trunk conductors 219 and 220. With the shunt removed from the upper wind:

ings of relays 312,313 and 314 the upper and lower windings of these relays are connected in series across the trunk conductors 310 and 311, their-resistance being so high thatthe coin pilot lamp relay 510 at the cord circuit cannot operate. Relay 312 being operated maintains rela s 304 and 306 energized.

When the -rel iiy 302 operated to connect the refunding current source 321 to the trunk conductors 219 and 220-since these conductors are now both connected directly through to the conductors of the subscribers line, current from source 321 flows through the coin box magnet 128 in such a direction as to cause the deposited coin to be dropped into the refund chute. Since it has been assumed that a coin has been deposited, the current flowing from source 321 operates relay 322 which replaces the shunt around the. upper windings of rev lays 312, 313 and 314 which was previously removed when relay 316 operated. The I shunting of these relay windings now permits sufiicient current to flow through the winding of relay 510 to operate the latter relay to light (III the coin pilot lamp 512 as a signal that the a coin has been refunded.

The operatorthereupon releases the refund key 508,'releasing relays 506, 409 and 405. Signaling battery and round are now reconnected to the trunk con uctors 406 and 407 and the volt source 511 is disconnected. Since relay 313 will not respond. to

0ollectz'ny the deposited coin. I

It will now be assumed that the o erator depressed the collect ke 513 rather t an the refund key 508'. The epression of key 513 operates rela 506 as before and connects the source 514 0 positive 110 volt coin collecting current through the windin of relay 515 over the outer right contact of icy 513, the

302 released relay 300 again energizes restor- III III

normal contact of key'508, thence through the a front contacts of relay 506, and as traced through the windings of relay 409, to ground. Relay 409 functions as previously described to operate rela 405 which in turn establishes connections w ereby current .flows from the source 514, through the lower windings of relays 312, 313 and 314, to ground at the upper front contact of relay 405. Relay 312"and olarized relay 314 now energize.' Relay 313 mg poled the opposite direction does not operate. Relay 312 holds relays 304 306 operated and relay 314 closes an obvious circuit for relay 317 which in turn closes an ob vious circuit for relay 302 and connects the source 323 of 110 volt positive coin collecting current to the ti and ring conductors of the calling line there y causing the coin box magnet 128 to collect the deposited coin.

At the cord circuit when the key 513 was depressed an obvious circuit was also closed for relay 504 which at its innermost lower front contact prepared a circuit for the lamp 512. If a coin was deposited in the coin box the relay 322 operated upon the application of collecting source 323 to the calling line and in the manner previously described causes the shunting of the upper windings of relays 312, 313 and 314 to permit the coin pilot relay 515 to operate. The circuit of lamp 512 is now completed from battery, through lamp 512, front contact of relay 515, inner right contact of key 513, to ground at the innermost lower front contact of relay 504.

Noting the illumination of the coin pilot lamp 512 the operator restores the collect key 513, releasing relay 506 thereby restoring the connection of the signalingcurrent source to the cord circuit and disconnecting the source of collecting current 514. Relays-409, 405, 312, 314, 317 and 302 thereupon release and the circuits are in condition for talking.

Supmision of connection.

in the bridge of trunk conductors 310 and 311. Relay 404 thereupon releases opening the shunt about the windings of relay 409 whereby these windings are effective in the bridge across conductors 406 and 407. Relay 503 at the cord circuit does not now receive suflicient current to maintain itself energized and it releases, opening the shunt about the supervisory lamp 502 to light the lamp as v a disconnect signal.

In response to this signal the operator re moves the plug 500 from the jack 403. Relay 401 thereupon releases disconnecting the windings of relay 404 from trunk conductors 310 and 311 and connecting the winding of relay 400 in bridge thereof. Relay 312 thereupon releases and since relay 300 is deenergized at this time the holding circuits for relays 304, 306, and 309 are opened and these relays release. 'Relay 304 upon releasing disconnect-s ground from conductor 305 releasing relay 201 in the first selector and removing ground from conductor 207.

At the selector a circuit is now closed from ground at the upper back contact of relay 201, over the back contacts of relays 200 and 204, off-normal contacts 221 to battery through the release magnet 222. Magnet 222 operates restoring the selector to normal. When the switch shaft reaches its normal position the contacts 221 open and magnet 2 22 releases.

When ground was removed from conductor 207, relays 106, 107, 108, 113, 124, 126 and 127 released and since relays 111 and 112 released upon the deenergization of relay 125, all apparatus associated with the t-runkcircuit of Fig- 1 is released. The release of relays 111 and 107 removes ground through retard coil 129, from sleeve conductor 130, which ground has held the line switch 101 operated, and the line switch releases. All apparatus employed in the establishment of the connection is now restored to normal.

Had the operator disconnected the cord circuit from the trunk jack 403 before the calling 404 from the trunk conductors 310 and 311,

reconnecting the winding of relay 400 in bridge of the trunk conductors. Relay 312 thereupon releases, releasing relays 303, 306 and 309. Upon the release of relay 309, relay 306 reoperates from ground at the front contact of relay 304, relay 304 being maintained energized by ground at "the front contact of relay 300. Relay 307 is now operated and connects the windings of relays 309 1 to the trunk conductors 310 and 311 thereby operating relay 400 which in turn closes the circuit of the trunk lamp 402. When the calling subscriber hangs up, relay 300 releases in turn releasing relay 304 whereupon the circuits all become restored in the manner pre-,

viously described.

Only those portions of Fig. 1 and Fig. 5 have been described herein whose functions are necessary to an understanding of the present invention. For a further description of the operation of the circuit of Fig. 1, reference may be had to the patent to Dunham 1,569,623, issued January 12, 1926.

What is claimed is:

1. In a telephone exchange system, a calling line, a coin box thereon, an operators position, a trunk circuit terminating thereat, means for extending said calling line to said trunk circuit, a cord circuit at said position for connection with said trunk circuit, coin box control keys associated with said cord circuit, a bridge across said trunk circuit comprising a plurality of relays, said relays being controlled by said keys, and meansunder the control of said relays for applying coin box operating current to said calling line:

2. In a telephone exchange system, a call-.

means for extending said calling line to said trunk circuit, a cord circuit at said position for connection with said trunk circuit, coin box control keys associated with said cord circuit for applying current of coin box operating voltage to said trunk circuit, a bridge across said trunk circuit comprising polarizedrelays responsive only to said coin box operating current and a relay responsive to current of signaling strength, means con trolled by said latter relay for controlling the release of said line extending means, and means controlled by said polarized relays for applying coin box operating current to said calling line.

3. In a telephone exchange system, a calling line, a coin box thereon, an operators position, a trunk terminating thereat, means for extending said calling line to said trunk circuit, a cord circuit at said position for connection with said trunk circuit, a coin box control key associated with said cord circuit for applying coin box operating current to said trunk circuit, a pilot lamp associated with said key, a high resistance bridge across said trunk circuit comprising a relay, said relay being controlled by said key, means under the control of said relay for applying coin box operating current to said calling line, and means operative upon the application of said current to said' line to reduce the resistance of said bridge to operate said pilot lamp.

4. In a telephone exchange system, a calling line, a coin box thereon, an operators position, a trunk circuit terminating thereat, means for extending said calling line to said trunk circuit, a cord circuit at said position for connection with said trunk circuit, a source of coin box operating current, a pilot relay, a coin box control key for connecting said source through said relay to said trunk circuit, a pilot lamp controlled by said relay, :1 high resistance bridge across said trunk circuit comprising a relay, said relay being controlled b said key, means under the control of said atter relay for applying coin box operating current to said calling line, and means operative upon the appllcation of sald current to said line to reduce the resistance of said bridge to operate said pilot relay,

5. In a telephone exchange system, a calling line, a coin box thereon, an operators position, a trunk circuit terminating thereat, means for extending said calling line to said trunk circuit, a cord circuit at said position for connection with said trunk circuit, coin collect and refund keys associated with said cord circuit for applying coin box operating current of opposite polarities to saidtrunk circuit, a pilot lamp associated with said ke s, a high resistance bridge across said circult comprising two oppositely polarized re lays, each of said relays bemg controlled respectively by one of said keys, means under the control of said relays for applying op erating current to said line for collecting or refunding coins deposited in said coin box, and means operative upon the application of said current to said line to reduce the resistance of said bridge to operate the pilot lamp.

6. In a telephone exchange system, a calling line, a coin box thereon, an operators position, a trunk circuit terminating thereat, said trunk circuit being inductively divided into a plurality of sections, means for ex tending said calling line to said trunk circuit, a cord circuit at said position for connection with said trunk circuit, a coin box control key associated with said cord circuit, a relay bridged across said trunk circuit at its incoming end and responsive to Said key, a bridge across said trunk circuit at its outgoing end including a relay, means under the control of said last named relay for applying coin box operating current to said calling line, and means controlled by said first relay to extend a-conductive connection from said key over both sections of said trunk circuit whereby said second relay is placed under the control of said key. I

7. In a telephonevexchange system, a calling line, a coin box thereon, an operators position, a trunk circuit terminating thereat, means for extending said calling line to said trunk circuit, a cord circuit at said position for connection with said trunk circuit, a supervisory rela in said cord circuit, a coin box control ey associated with said cord circuit, a bridge including a relay connected across said trunk circuit for controlling said coin box, said bridged relay being responsive to current of coin box operating voltage applied by said key but unresponsive to current of signaling voltage applied through said supervisory relay from said cord circuit and having such resistance that said supervisory relay does not operate in series therewith, and means responsive to the removal of the subscribers receiver from the switchhook for reducing the resistance of said bridge whereby said supervisory relay operates.

8. In a telephone exchange system, a callin line, an operators position, a trunk circult for extending said line to said position, a trunk lamp, a bridged relay at the incomin end of said trunk circuit for controlling sai lamp, means for establishing a battery bridge acrom said trunk circuit at its outgoingend upon seizure of said trunk circuit by said subscribers line to operate said relay, a relay in said battery bridge inoperative in circuit with said first relay, means operative upon the connection of said operators position to the incoming end of said trunk circuit to disconnect said first relay from said trunk circuit and vto connect a battery bridge there- Ill to, whereby said second relay operates, a relay bridge at the outgoin end of said trunk circuit established upon t e response of said second relay, and a third relay under the 5 control of said latter bridge for holding said second relay operated, whereby if said trunk is released at said incoming end before the subscriber releases said second relay deenergizes and said first relay reenergizes to reoperate said trunk lamp.

In witness whereof, I hereunto subscribe my name this 3rd day of December, A. D.

FREDERICK R. LAMBERTY. 

